1. Field of the Invention
The invention relates to amino-functional photopolymer compositions containing photosensitizers which upon irradiation in the presence of ordinary molecular oxygen become cured. By selective irradiation, the photopolymer compositions lend themselves to use in photo-oxidation imaging processes which are also within the scope of the invention.
2. Description of the Prior Art
The prior art is replete with disclosures of photopolymers which are curable, cross-linkable or photopolymerizable upon exposure to irradiation. A variety of catalytic free-radical mechanisms have been postulated to explain the chemistries of many of these photopolymerization processes. Such photo-initiated, free-radical, photopolymerization, imaging processes generally are inhibited by the presence of molecular oxygen in contrast to the photo-oxidation imaging process of the present invention, where the presence of molecular oxygen is a requisite.
There have also been prior teachings of photopolymerizable systems in which the photopolymer may contain an amine moiety.
U.S. Pat. No. 3,914,165, Gaske, relates to a photopolymer system based on Michael addition reaction products. An amine containing at least one amino hydrogen atom is adducted with an excess of ethylenic material comprising a polyacrylate to form an adduct containing unreacted acrylate groups and at least one tertiary beta amino group. The radiation cure realized with the Gaske photopolymer is not based primarily on amino-functionality, but relies on an excess of unreacted ethylenic unsaturation which enables subsequent photopolymerization under the influence of well-known photo-initiators and ultraviolet radiation. Thus, the Gaske disclosure does not teach a photopolymer system wherein photo-oxidation of amino-functionality is relied upon to effect the cure or other physical change in the photopolymer.
U.S. Pat. No. 3,533,796, Lassig, discloses a light-sensitive material comprising a polymer which contains N-methylol ester units or N-methylol ether units of acrylamide or methacrylamide in combination with a compound capable of giving off hydrogen ions under the influence of light. The polymers cross-link by acid hydrolysis of the ether or ester groups to form methylol groups which immediately give rise to inter-molecular condensation.
Two U.S. Pat. Nos. 3,876,518 and 3,878,077, both issued to Borden, et al., relate to acrylated epoxidized soybean oil amine compounds. According to the patents, an epoxidized soybean oil is acrylated and subsequently reacted with an amine compound. The resulting amine derivative is photo-curable with high-energy ionizing radiation or, when acylyl or methacrylyl groups are present, with well-known photo-initiators and ultraviolet radiation.
U.S. Pat. No. 3,697,274, Herrmanns, discloses an acid-curable amine-formaldehyde resin. Coatings of this resin are photo-curable only when they contain a light-sensitive halogen compound.
U.S. Pat. No. 3,512,971, Floss, et al., discloses a photo-curable composition based on a mixture of polyamides with photopolymerizable bis-acrylamide and well-known photo-initiators.
The prior art does not disclose a photopolymer system which relies primarily on the presence of amino groups to cross-link or otherwise physically change or photo-cure the photopolymer composition. To the extent that the prior art describes some form of amino-functionality in photopolymer compositions, the disclosures are limited to photo-curing mechanisms which rely on the presence of other active ingredients or functionality in order to effect photo-cross-linking or photo-curing of the polymer system. In any event, the prior art does not describe photo-oxidation curing or photo-oxidation imaging of amino-functional polymers.
Photo-oxidation processes for imaging polymer films have been described in a number of issued U.S. patents--e.g., U.S. Pat. Nos. 3,790,389, Heimsch, et al., 3,801,320, Erickson, 3,847,609 and 3,926,648, both of Breslow, et al., and 3,846,266, Duinstee, et al. The processes disclosed in the foregoing patents achieve photoimaging by the photo-oxidation of --C.dbd.C-- unsaturation in polymer films by exposure in the presence of oxygen and a photosensitizer. The photo-oxidation results in the production of hydroperoxides attached to the polymer chain at the site of the allylic unsaturation. The latent hydroperoxide polymer image may then be amplified and/or developed by a variety of techniques. Polymers containing sulfur-functionality which can be imaged by photo-oxidation processes are also described in pending U.S. Pat. application Ser. No. 756,034, Kern, now abandoned.
The present invention does not depend for imaging upon the hydroperoxidation of --C.dbd.C-- unsaturation or on the oxidation of sulfur-functionality, but on available amino-functionality. The copresence of carbon-to-carbon unsaturation and/or sulfur-functionality in the amino-functional photopolymer or in other polymers present in the composition is not excluded from the present invention and, in some instances, may be beneficial, but it should be understood that the invention does not depend on the presence of carbon-to-carbon unsaturation or sulfur-functionality.